Iterative approach for removing middle points in a linked list of line segments
Last Updated : 27 Jan, 2023
This post explains the iterative approach of this problem.
We maintain two pointers, prev and temp. If these two have either x or y same, we move forward till the equality holds and keep deleting the nodes in between. The node from which the equality started, we adjust the next pointer of that node.
Implementation:
C++ // C++ program to remove intermediate // points in a linked list that represents // horizontal and vertical line segments #include <iostream> using namespace std; // Node has 3 fields including x, y // coordinates and a pointer to next node struct Node { int x, y; struct Node *next; }; /* Function to insert a node at the beginning */ void push(struct Node **head_ref, int x, int y) { struct Node *new_node = new Node; new_node->x = x; new_node->y = y; new_node->next = (*head_ref); (*head_ref) = new_node; } /* Utility function to print a singly linked list */ void printList(struct Node *head) { struct Node *temp = head; while (temp != NULL) { printf("(%d, %d)-> ", temp->x, temp->y); temp = temp->next; } printf("\n"); } // This function deletes middle nodes in a // sequence of horizontal and vertical line // segments represented by linked list. void delete_Middle_Nodes(Node *head) { Node *temp = head->next, *prev = head; while (temp) { // checking equality of point x if (temp->x == prev->x) { Node *curr = prev; prev = temp; temp = temp->next; // removing vertical points of line // segment from linked list while (temp && temp->x == prev->x) { curr->next = temp; free(prev); prev = temp; temp = temp->next; } } // checking equality of point y else if (temp->y == prev->y) { Node *curr = prev; prev = temp; temp = temp->next; // removing horizontal points of line // segment from linked list while (temp && temp->y == prev->y) { curr->next = temp; free(prev); prev = temp; temp = temp->next; } } else { prev = temp; temp = temp->next; } } } // Driver program to test above functions int main() { struct Node *head = NULL; push(&head, 40,5); push(&head, 20,5); push(&head, 10,5); push(&head, 10,8); push(&head, 10,10); push(&head, 3,10); push(&head, 1,10); push(&head, 0,10); printf("Given Linked List: \n"); printList(head); delete_Middle_Nodes(head); printf("Modified Linked List: \n"); printList(head); return 0; } class LinkedList { Node head; // head of list /* Linked list Node*/ class Node { int x,y; Node next; Node(int x, int y) { this.x = x; this.y = y; next = null; } } // This function deletes middle nodes in a sequence of // horizontal and vertical line segments represented // by linked list. private void delete_Middle_Nodes(Node head) { Node prev = head; Node temp = head.next; while (temp != null) { // checking equality of point x if (temp.x == prev.x) { Node curr = prev; prev = temp; temp = temp.next; // removing vertical points of line // segment from linked list while (temp != null && temp.x == prev.x) { curr.next = temp; prev.next = null; prev = temp; temp = temp.next; } } // checking equality of point y else if (temp.y == prev.y) { Node curr = prev; prev = temp; temp = temp.next; // removing horizontal points of line // segment from linked list while (temp != null && temp.y == prev.y) { curr.next = temp; prev.next = null; prev = temp; temp = temp.next; } } else { prev =temp; temp = temp.next; } } } /* Given a reference (pointer to pointer) to the head of a list and an int, push a new node on the front of the list. */ void push(int x, int y) { /* 1 & 2: Allocate the Node & Put in the data*/ Node new_node = new Node(x,y); /* 3. Make next of new Node as head */ new_node.next = head; /* 4. Move the head to point to new Node */ head = new_node; } void printList() { Node temp = head; while (temp != null) { System.out.print("(" + temp.x + "," + temp.y + ")->"); temp = temp.next; } System.out.println(); } /* Driver code */ public static void main(String args[]) { LinkedList llist = new LinkedList(); llist.push(40,5); llist.push(20,5); llist.push(10,5); llist.push(10,8); llist.push(10,10); llist.push(3,10); llist.push(1,10); llist.push(0,10); System.out.println("Given list"); llist.printList(); llist.delete_Middle_Nodes(llist.head); System.out.println("Modified Linked List is"); llist.printList(); } } // This code is contributed by shubham96301. # Python3 program to remove intermediate # points in a linked list that represents # horizontal and vertical line segments import math # Node has 3 fields including x, y # coordinates and a pointer to next node class Node: def __init__(self, x, y): self.x = x self.y = y self.next = None # Function to insert a node at the beginning def push(head_ref, x, y): new_node = Node(x, y) new_node.x = x new_node.y = y new_node.next = head_ref head_ref = new_node return head_ref # Utility function to print # a singly linked list def printList(head): temp = head while (temp != None): print("(", temp.x, ",", temp.y, ")", end = "->",) temp = temp.next print() # This function deletes middle nodes in a # sequence of horizontal and vertical line # segments represented by linked list. def delete_Middle_Nodes(head): temp = head.next prev = head while (temp): # checking equality of point x if (temp.x == prev.x): curr = prev prev = temp temp = temp.next # removing vertical points of line # segment from linked list while (temp != None and temp.x == prev.x): curr.next = temp #free(prev) prev = temp temp = temp.next # checking equality of point y elif (temp.y == prev.y): curr = prev prev = temp temp = temp.next # removing horizontal points of line # segment from linked list while (temp != None and temp.y == prev.y): curr.next = temp #free(prev) prev = temp temp = temp.next else: prev = temp temp = temp.next # Driver Code if __name__=='__main__': head = None head = push(head, 40, 5) head = push(head, 20, 5) head = push(head, 10, 5) head = push(head, 10, 8) head = push(head, 10, 10) head = push(head, 3, 10) head = push(head, 1, 10) head = push(head, 0, 10) print("Given Linked List: \n", end = "") printList(head) delete_Middle_Nodes(head) print("Modified Linked List: \n", end = "") printList(head) # This code is contributed by AbhiThakur // C# program to remove intermediate // points in a linked list that represents // horizontal and vertical line segments using System; public class LinkedList { public Node head; // head of list /* Linked list Node*/ public class Node { public int x,y; public Node next; public Node(int x, int y) { this.x = x; this.y = y; next = null; } } // This function deletes middle nodes in a sequence of // horizontal and vertical line segments represented // by linked list. private void delete_Middle_Nodes(Node head) { Node prev = head; Node temp = head.next; while (temp != null) { // checking equality of point x if (temp.x == prev.x) { Node curr = prev; prev = temp; temp = temp.next; // removing vertical points of line // segment from linked list while (temp != null && temp.x == prev.x) { curr.next = temp; prev.next = null; prev = temp; temp = temp.next; } } // checking equality of point y else if (temp.y == prev.y) { Node curr = prev; prev = temp; temp = temp.next; // removing horizontal points of line // segment from linked list while (temp != null && temp.y == prev.y) { curr.next = temp; prev.next = null; prev = temp; temp = temp.next; } } else { prev =temp; temp = temp.next; } } } /* Given a reference (pointer to pointer) to the head of a list and an int, push a new node on the front of the list. */ void push(int x, int y) { /* 1 & 2: Allocate the Node & Put in the data*/ Node new_node = new Node(x,y); /* 3. Make next of new Node as head */ new_node.next = head; /* 4. Move the head to point to new Node */ head = new_node; } void printList() { Node temp = head; while (temp != null) { Console.Write("(" + temp.x + "," + temp.y + ")->"); temp = temp.next; } Console.WriteLine(); } /* Driver code */ public static void Main(String []args) { LinkedList llist = new LinkedList(); llist.push(40,5); llist.push(20,5); llist.push(10,5); llist.push(10,8); llist.push(10,10); llist.push(3,10); llist.push(1,10); llist.push(0,10); Console.WriteLine("Given list"); llist.printList(); llist.delete_Middle_Nodes(llist.head); Console.WriteLine("Modified Linked List is"); llist.printList(); } } /* This code contributed by PrinciRaj1992 */ <script> // JavaScript program to remove intermediate // points in a linked list that represents // horizontal and vertical line segments var head = null; // head of list /* Linked list Node*/ class Node { constructor(x, y) { this.x =x; this.y = y; this.next = null; } } // This function deletes middle nodes in a sequence of // horizontal and vertical line segments represented // by linked list. function delete_Middle_Nodes(head) { var prev = head; var temp = head.next; while (temp != null) { // checking equality of point x if (temp.x == prev.x) { var curr = prev; prev = temp; temp = temp.next; // removing vertical points of line // segment from linked list while (temp != null && temp.x == prev.x) { curr.next = temp; prev.next = null; prev = temp; temp = temp.next; } } // checking equality of point y else if (temp.y == prev.y) { var curr = prev; prev = temp; temp = temp.next; // removing horizontal points of line // segment from linked list while (temp != null && temp.y == prev.y) { curr.next = temp; prev.next = null; prev = temp; temp = temp.next; } } else { prev =temp; temp = temp.next; } } } /* Given a reference (pointer to pointer) to the head of a list and an int, push a new node on the front of the list. */ function push(x, y) { /* 1 & 2: Allocate the Node & Put in the data*/ var new_node = new Node(x,y); /* 3. Make next of new Node as head */ new_node.next = head; /* 4. Move the head to point to new Node */ head = new_node; } function printList() { var temp = head; while (temp != null) { document.write("(" + temp.x + ", " + temp.y + ") -> "); temp = temp.next; } document.write("<br>"); } /* Driver code */ push(40,5); push(20,5); push(10,5); push(10,8); push(10,10); push(3,10); push(1,10); push(0,10); document.write("Given list:<br>"); printList(); delete_Middle_Nodes(head); document.write("Modified Linked List is:<br>"); printList(); </script> OutputGiven Linked List: (0, 10)-> (1, 10)-> (3, 10)-> (10, 10)-> (10, 8)-> (10, 5)-> (20, 5)-> (40, 5)-> Modified Linked List: (0, 10)-> (10, 10)-> (10, 5)-> (40, 5)->
Time complexity: O(N) where N is no of nodes in given linked list
Auxiliary Space: O(1)
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